This invention relates forming of a double seam between an end wall of a can and a body of a can and more particularly, but not exclusively to the forming of a double seam, of small dimensions, fixing a can end to a can end shell and can end permitting the drawn and wall ironed can body.
Wall ironed can bodies commonly have a bottom wall and an integral side wall upstanding from the periphery of the bottom wall to terminate in a shoulder, neck of reduced diameter, and an outwardly directed flange. It is usual for the majority of the side wall to be about half the thickness of the bottom wall so that work hardening is minimized to permit forming of the flange and double seam. An annulus of arcuate cross-section connects the neck to the flange a typical radius of this arcuate annulus is 0.050". Wall ironed can bodies are usually coated internally after forming by sprayed lacquer. Can ends fitted to these wall ironed can bodies are stamped from precoated sheet metal such as tinplate, electrochrome coated steel (TFS), or aluminium alloy so that hitherto the tightness of the contours of the can end have been limited by the limits of lacquer adhesion during stamping and the severity of the deformation in the press tool. When can bodies had a 206 diameter neck with 0.050" flange radius it was usual for the seaming panel radius of the can end to be 0.080" so that there was risk that a short overlap of cover hook and body hook arises on the double seam. The usual remedy was to increase base pressure to about 160 lbs on the can end during double seaming at risk of crushing the thin side wall of the can body.
For reasons of economy the can industry is now asked to provide cans with a neck diameter reduced to about 2" (50 mm) made with thinner side walls. There also arises a problem of designing a shaped can end that will permit formation of smaller double seams from thinner metal without risk of peripheral collapse to folds in the force edge of the can end.